Controlling the Speed of Light-Activated Colloids with a Constant, Uniform Magnetic Field

It is demonstrated how the strength of activation for photocatalytic, self-propelled colloids can be enhanced with a constant, uniform magnetic field. When exposed to ultraviolet light and hydrogen peroxide, the titanium dioxide-based colloids become actively propelled. Due to the iron oxide core, a uniform field oriented perpendicular to the surface where motion takes place causes the asymmetrically shaped particles to rotate, which consequently leads to an increase in activity. The field-dependent dynamics of self-propulsion is quantified, and a qualitative description of how this effect arises is proposed. Since the application of the field is easily reversible, modulating the field on-and-off serves as a de facto “switch” that controls particle behavior.